In-situ combustion is an established method for enhanced oil recovery. In a typical application, air is injected into a vertical well resulting in combustion and increased oil mobility. Product oil is then recovered via either the injection well by a process known as “huff-and-puff” or via a second vertical well. The process is not widely used because it has been difficult to control. Thus, attempts have been made to improve the process.
To reduce the problem of gravity segregation, for example, air is injected at a high point of the reservoir. U.S. Pat. No. 5,211,230 to Ostapovich discloses injecting air at a high point of the reservoir via a vertical well along with a lower horizontal production well. U.S. Pat. No. 5,626,191 to Greaves discloses placing the low horizontal well perpendicular to the vertical well to draw the combustion front along the horizontal well and away from the injection well. Although this is an improvement, combustion products are intended to be removed with the heated oil and thus injected fresh air also has ready access to the horizontal well between the toe and the combustion front. A further disadvantage is that the injection well and the horizontal well vertical leg must be located far apart. Accordingly, there is still a need for a process which is controllable and provides efficient use of injected air.
It is an object of the present invention to provide an improved method of contacting an injected fluid with a reaction front whereby oil may be recovered economically. It is a further object of the present invention to enable more efficient in-situ combustion of in-place heavy oil whereby combustion products are more efficiently removed from the combustion zone and thermal cracking is promoted.